System and method for measuring and correcting astigmatism using laser generated corneal incisions

ABSTRACT

A laser system that includes a laser source emitting a laser beam along an axis and a keratometer. The keratometer includes a first set of individual light sources that are equally spaced from one another along a first ring and that direct a first light toward an eye and a second set of individual light sources that are equally spaced from another along a second ring and direct a second light toward the eye, wherein the first ring and said second ring are co-planar and concentric with one another about the axis. The laser system includes a telecentric lens that receives the first light and second light reflected off of the eye and a detector that receives light from the telecentric lens and forms an image. The laser system also includes a processor that receives signals from said detector representative of the image and determines an astigmatism axis of the eye based on the signals.

This application is a continuation of Ser. No. 13/427,130 filed Mar. 22,2012, which application claims the benefit of priority under 35 U.S.C. §119(e)(1) of 1) U.S. Provisional Application Ser. No. 61/467,592, filedMar. 25, 2011 and 2) U.S. Provisional Application Ser. No. 61/467,622,filed Mar. 25, 2011, and is a continuation-in-part application of U.S.patent application Ser. No. 13/017,499, filed Jan. 31, 2011, whichclaims the benefit of priority under 35 U.S.C. § 119(e)(1) of U.S.Provisional Application Ser. No. 61/300,129, filed Feb. 1, 2010, theentire contents of each of the above mentioned patent applications andprovisional applications is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a system for performing an astigmatismmeasurement for the purpose of correcting astigmatism. The presentinvention also has to do with marking the measured axis of astigmatismwith a laser-created mark.

BACKGROUND

In known procedures for correcting astigmatism, such as limbal relaxingincisions, LASIK or implantation of toric IOLs, it is important toregister the respective treatment or device in precise alignmentrelative to the eye's axis of astigmatism. The astigmatism is firstmeasured by a benchtop corneal topographer, such as the Humphrey Atlascorneal topographer manufactured by Zeiss of Dublin, Calif. or akeratometer, such as the LenStar keratometer manufactured by Haag Streitof Bern, Switzerland. The patient's eye is manually marked with an inkmarker to indicate the axis of astigmatism or a reference horizontalaxis or other axis from which the astigmatism axis can be laterreferenced.

While each of the previously mentioned correction procedures isperformed with the patient in a reclining position, the priorastigmatism measurement with the benchtop instrument ande and themarking of the patient's eye are performed with the patient in a sittingposition. During the process of the patient being moved from the sittingposition to the reclining position, cyclotorsion (rotation of the eyeabout its optical axis) generally occurs. The registration marker isused when the patient is in the reclining, treatment position to adjustfor any rotation of the axis of astigmatism which might occur.

The use of ink marks reduces the effect of cyclotorsion on theastigmatism treatment; however, it is inconvenient—for best results, itrequires a separate seating of the patient at a slit lamp—but still haslimited accuracy because of the inevitable errors in manually placingthe initial marks, and the “bleeding” of the marks as the tear filmreacts with the marking ink.

The use of ink marks is avoided by the Placido ring measurement systemdescribed in U.S. patent application Ser. No. 13/017,499 (“the '499application”), the entire contents of which are incorporated byreference. With the Placido ring system, the images of the reflectionsof Placido rings are in the form of circular or elliptical bands, withsharp, high contrast edges which allow the image analysis software inthe system to accurately find the edges of each reflected circular orelliptical band. The found edges are curve fit to an ellipse. Thereflections are circular (i.e. an ellipse of eccentricity equal to 0) ifthe cornea has no astigmatism. If the cornea does have some astigmatism,the clock angle of the minor axis of the elliptical image, gives theorientation of the axis of astigmatism. The clock angle is measuredrelative to a polar coordinate defined such that 0° is in the nasaldirection; 90° is superior and 180°, temporal. The length of the majorand minor axes of the ellipses provides the information from which themagnitude of the spherical power and cylindrical power (astigmatism) ofthe cornea is derived.

The Placido ring invention disclosed in the '499 application allows forthe astigmatism axis to be measured while the patient is laying on agurney under the laser so no manual measurement or marking of the eye isneeded. (If a toric IOL is to be used during the corrective procedure,the laser cuts a reference mark into the capsulotomy allowing thesurgeon to accurately position the clock angle of the IOL to the axis ofastigmatism measured by the laser. If LRIs are to be used during thecorrective procedure, the laser uses the Placido ring/keratometermeasurement of axis to orient the LRIs to the correct clock angle.)

One issue regarding the Placido ring invention described in the '499application is that it does not take into account that variouspreoperative measurement instruments, measuring the same parameters,generate different values of the parameters because of differencesbetween the measurement principles, implementation of engineering, etc.,of different instruments.

As an illustration of the variability in the value of measuredparameters, let us take a look at a cataract procedure. In such aprocedure, a number of preoperative measurements are made of thepatient's eye in order to select the correct IOL for the patient. Amongthese measurements are measurements of the K values and axis ofastigmatism of the patient's cornea. The K values are the optical power,in Diopters, of the steep axis (axis in the plane perpendicular to theoptic axis which has the highest lens curvature) and shallow axis (axisin the plane perpendicular to the optic axis which has the least lenscurvature). The “clock” angle of the steep and shallow axes areconventionally measured in degrees from 0° to 180° in an angularcoordinate system perpendicular to and centered on the optic axis of theeye. From the point of view of an optometrist or ophthalmologist lookingat the patient, 0° is to the right, on the nasal/temporal axis. Thescale proceeds counterclockwise from 0° to 180°. The difference betweenthe K value of the steep and shallow axes is the magnitude of theastigmatism of the eye. The angle of the steep axis, measured on thecoordinate system described above is the axis of astigmatism. The Kvalues and axis of astigmatism are used, along with other measurementsof the eye, in one of several common IOL power formulae (ref) todetermine the proper IOL optical power to be used for the patient.

A typical cataract procedure using a laser system can involve thefollowing processes: making preoperative measurements of the patient'seye for selection of the power and other characteristics of the IOL,placement of the patient on a gurney under the laser, measuring thepatient's axis of astigmatism by an integral astigmatism axismeasurement system built into the laser, docking the patient's eye tothe laser, performing the laser treatment, including LRIs or capsulotomywith tagged astigmatism axis if the patient's astigmatism is to betreated, retracting the laser head, removing the patient's cataractouslens and implanting an IOL is implanted. Post-operatively, the patient'ssurgically repaired eye is refracted by determining the amount ofrefractive correction needed to bring the patient's vision to itssharpest distance focus. The refraction can be measured in the sameunits as those used by the preoperative measurements of the patient'scornea, i.e., Diopters of curvature along the steep and shallow axes andaxis of astigmatism. These values are generally converted via simplemathematical relationships to the magnitudes of the residual sphericaland cylindrical power of the eye and the axis of astigmatism. However,the refraction measures ocular, rather than corneal optical power, i.e.,the optical power of the whole eye including the newly implanted IOL,rather than just the corneal optical power as was measuredpreoperatively. In most cases, a surgeon intends to select an IOL whichbrings the patient's vision as close as possible to perfect focus fordistance vision, i.e., to bring the patient's residual optical power tozero or near zero for both the spherical and cylindrical components ofthe optical power.

A cataract surgeon may monitor the post-operative refractions of his orher patients, grouped by which type or design of IOL is used. If thereis a bias in the clinical outcomes for a particular type of lens, forexample: patients implanted with lens Type A have an average residualspherical power of 0.5 Diopters, an adjustment parameter called a “lensconstant” used in the IOL power formula is changed to allow the adjustedformula to more accurately select IOL power for future patients. Thelens constant adjustment is intended to compensate for a number offactors which can affect clinical refractive outcomes. The mostimportant of these factors is a combination of variation in surgicaltechnique and characteristics of a particular design of IOL which affectwhere along the anterior/posterior axis of the eye the IOL will tend toposition itself and which therefore directly influences the refractiveoutcome. However, the lens constant also implicitly accounts fordifferences in pre- and post-operative measurement techniques and, inparticular, the type of instrument used to measure the K values and axisof astigmatism, which, as mentioned above, vary from instrument toinstrument. For example, a keratometer which consistently measures Kvalues a bit higher than normal would tend to cause an IOL of higherthan required power to be selected for a treatment. Once this bias wasdetected (by post-operative measurements showing that patients tended tobe overcorrected by that type of IOL as used by a particular surgeonemploying that particular keratometer and other surgical procedurecharacteristics), the lens constant for that type of IOL (as used bythat surgeon, procedure, etc.) would be adjusted to eliminate the bias.

It is helpful for this discussion to differentiate between systematicand random measurement error. Random error occurs with any type ofinstrumental measurement but can be reduced to an arbitrarily smallmagnitude by averaging a sufficient number of repeated measurements.Systematic error between instruments is due to fundamental differencesin measurement technique, calibration, etc. and represents anirreducible bias between the two instruments. No amount of averaging ofrepeated measurements can eliminate the bias.

The foregoing process or measuring performed pre- and post-operativelyand adjusting the lens constant to improve clinical refractive outcomesworks well if a surgeon's surgical technique is consistent fromcase-to-case and if all other aspects of the surgical procedure. Forexample, use of a particular type of keratometer to measure K values andaxis of astigmatism are likewise consistently followed. However, thislatter condition is not always met. For example, a surgeon may treatpatients at more than one hospital or clinic, each of which uses adifferent instrument to measure K values and axis of astigmatism. Inthis case, different lens constants could be used for eachsurgeon/clinic combination to correctly account for differences inrefractive outcomes related to practices at each hospital or clinic, or,more likely, a single lens constant would be used across clinics eventhough a higher variability in clinical refractive outcomes wouldresult.

BRIEF SUMMARY

One aspect of the present invention regards a laser system that includesa laser source emitting a laser beam along an axis and a keratometer.The keratometer includes a first set of individual light sources thatare equally spaced from one another along a first ring and that direct afirst light toward an eye and a second set of individual light sourcesthat are equally spaced from another along a second ring and direct asecond light toward the eye, wherein the first ring and said second ringare co-planar and concentric with one another about the axis. Thekeratometer also includes a telecentric lens that receives the firstlight and second light reflected off of the eye and a detector thatreceives light from the telecentric lens and forms an image of theindividual light sources including the first and second lights. Thekeratometer further includes a processor that receives signals from saiddetector representative of the image and determines an astigmatism axisof the eye based on the signals.

A second aspect of the present invention regards a method of determiningproperties of an eye, the method including positioning an eye so that itreceives a laser beam that is emitted by a laser source beam along anaxis and generating first light toward the eye from a first set ofindividual light sources that are equally spaced from one another alonga first ring. The method including generating second light toward saideye from a second set of individual light sources that are equallyspaced from another along a second ring and direct a second light towardthe eye, wherein the first ring and the second ring are co-planar andconcentric with one another about the axis. The method further includingforming an image of light reflected off of the eye from the first lightand the second light and determining an astigmatism axis of the eyebased on the image. The laser source, the first set of individual lightsources and the second set of individual light sources are integrated ina common housing to allow the cyclotorsion of the eye which occursbetween preoperative measurement, which is performed with the patient ina sitting position and at the time or surgery, when the patient is lyingunder the laser. The incorporation of the laser and keratometer in acommon housing also allows the user to measure all patients with thesame measuring device so that systematic errors in determination of IOLlens constants are avoided or reduced.

A third aspect of the present invention regards a method of treating aneye, the method including positioning an eye so that it receives a laserbeam that is originally emitted by a laser source beam along an axis;and generating first light toward the eye from a first set of individuallight sources that are equally spaced from one another along a firstring. The method including generating second light toward said eye froma second set of individual light sources that are equally spaced fromanother along a second ring and direct a second light toward the eye,wherein the first ring and the second ring are co-planar and concentricwith one another about the axis. The method further including forming animage of light reflected off of the eye from the first light and thesecond light and determining an astigmatism axis of the eye based on theimage. The method further including controlling the laser beam so thatthe laser beam performs a cutting of the eye based on the astigmatismaxis.

One or more aspects of the present invention allow for measurement ofthe properties of an astigmatism axis of an eye.

One or more aspects of the present invention allow for reducing oreliminating systematic errors during measurement of the properties of anastigmatism axis of an eye.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawings, which are incorporated herein and constitutepart of this specification, and, together with the general descriptiongiven above and the detailed description given below, serve to explainfeatures of the present invention. In the drawings:

FIG. 1 schematically shows an embodiment of a measuring system formeasuring the corneal astigmatism axis prior to an ophthalmologicalprocedure being performed on the eye of a patient in accordance with thepresent invention;

FIG. 2 schematically shows operation of an embodiment of a telecentricdetection system for measurements of concentric rings of LEDs that isused with the measuring system of FIG. 1 in accordance with the presentinvention;

FIG. 3 shows an example of an image of light of concentric rings of LEDsas reflected off of a cornea and imaged by the telecentric detectionsystem of FIG. 2;

FIG. 4 shows picture of a common toric intraocular lens (IOL) implantedin an eye after the corneal astigmatism axis of the eye has beendetermined and marked using a treatment laser, using the measuringsystem of FIG. 1 in accordance with the present invention; and

FIG. 5 schematically shows laser cut capsulotomy openings in theanterior crystalline lens capsule cut with a “tag” to mark the axis ofastigmatism that is measured by the measuring system of FIG. 1 inaccordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically shows a measuring and treatment system 100 formeasuring the corneal astigmatism axis and for performing anophthalmological procedure on the eye 102 of a patient. The system 100includes a keratometer 250 which includes a light generator 203 (dashedlines) and a telecentric detection system 200. The light generator 203includes two light sources, each comprising a ring of 10-20 discreteLEDs 202. The telecentric detection system 200 is used for measuringconcentric rings of the LEDs 202 and for alignment of the patient's eyewith the keratometer. The system 100 also includes a Scheimpflug-basedlens and cornea locating system 300, and a treatment laser system thatincludes a treatment laser 104.

In use, the patient typically lies on a gurney or a reclining surgicalchair which is rolled into position under the optical head of thetreatment laser 104. The keratometer 250 and the Scheimpflug-based lensand cornea locating system 300 may be designed to work with the patientin a reclining position under the treatment laser system since in thisposition the cyclotorsion of the eye, which occurs when a patient who isin a sitting position (for example to allow conventional astigmatismmeasurements to be made) changes to a reclining position, has alreadyoccurred. It is also advantageous that the detection system 200 and theScheimpflug-based lens and cornea locating system 300 are so locatedsuch that the patient can remain stationary for both the measurementsand laser treatment, since this obviates or lessens the time consumingstep of re-aligning the patient with the laser for the subsequent lasertreatment.

After the corneal astigmatism axis is found using the measurement of theconcentric rings of LEDs 202, a medical procedure can be performed withthe laser systems described in U.S. patent application Ser. Nos.11/337,127; 12/217,285; 12/217,295; 12/509,412; 12/509,021; 12/509,211and 12/509,454, the entire contents of each of which are incorporatedherein by reference. Possible procedures to be performed by the lasersystems to correct or reduce astigmatism are the performance of limbalrelaxing incisions or LASIK. Another possible procedure is the use ofthe treatment laser to assist in cataract removal and IOL implantation.The treatment laser is also used to create a reference mark on theanterior capsule to allow the subsequent implantation of a toric IOL tobe correctly oriented with respect to the axis of astigmatism.

Operation of keratometer 250 includes having the patient lie on apatient bed in position for the laser surgery. The patient is instructedto stare at a red fixation light generated by fixation light source 225that is housed in the telecentric detection system 200. The fixationlight source 225 includes an LED which generates red light. The redlight is collimated and directed to a beam combiner 227 which reflectsthe light to mirror 220. The red light is then redirected toward the eyeof the patient so that the red light is aligned to be collinear with theaxis of the laser beam generated by laser 104 and centered at the middleof the concentric rings of LEDs 202, i.e., the axis of the keratometer.

Next, the optical head of the treatment laser 104 is aligned, using ajoystick that controls a 3-axis motion control system, to the patient'scornea. The optical head of the treatment laser system houses both thekeratometer 250 and the Scheimpflug-based lens and cornea locatingsystem 300 as well as the optics that are used to guide the treatmentlaser beam. Thus, aligning this optical head relative to the patientserves the purpose of aligning all three systems (200; 300 and treatmentlaser system) simultaneously relative to the patient's eye and, thus,reduces the need for time consuming re-alignments for the sequentialoperations. When the patient stares at the fixation light generated byfixation light source 225, and when the optical head of the treatmentlaser is aligned such that reflections of the two concentric rings ofLEDs 202 from the patient's cornea are centered within the patient'spupil, as visualized on the telecentric camera system 200, the patient'svisual axis is aligned with the keratometer 250 and treatment laser 104.A sensor, not shown, detects when the z position (position along adirection parallel to the axis of the laser beam passing through aconcentric rings of LEDs 202 of light generator 203 as shown in FIG. 1)is correct for the astigmatism axis measurement; the sensor generates asignal when the eye is at the correct distance below the light generator203. A software reticule is superimposed on the image of the eye on thetelecentric camera's monitor, to assist in the assessment of centration.

After the z-position for the optical head of the treatment laser 104 isdetermined, and the light generator 203 is centered directly above theeye then measurement of the astigmatism axis is performed usingtelecentric detection system 200 for measurements of concentric rings ofLEDs 202.

Telecentric system 200 is part of the keratometer 250, which is similarto the one manufactured and sold under the tradename LenStar LS-900 byHaag Streit of Bern, Switzerland. The keratometer 250 includes two setsof LEDs 202, wherein one set of 16 LEDs are equally spaced from oneanother along a first circle or ring. The second set of 16 LEDS 202 areequally spaced from one another along a second circle or ring. The firstand second circles are co-planar and concentric with one another andconcentric about the common optical axis of the fixation light source225 and treatment laser 104. The LEDs 202 are chosen to approximatepoint sources of light so that the images of the reflections of the LEDs202 from the cornea are as compact as possible and can be located on thecamera image as accurately and precisely as possible. Each set of LEDs202, as described above, is denoted as a ring source.

Operation of keratometer 250 is understood upon a review of FIGS. 2-3.As shown in FIG. 2, red light 260 from the fixation light source 225 isdirected by beam combiner 227 to the eye of the patient. When thepatient stares at the red light improved alignment of the patient's eyewith the axis of the keratometer 250 is achieved. While the patientstares at the red light 260, light 201 from one or more concentric ringsources of light generator 203 is directed towards the cornea of the eye102 and then reflected light 214 is directed towards an objective andtelecentric lens 204 of telecentric system 200. Note that the ringsources are concentric relative to an axis of the treatment laser beampassing through the opening of the light generator 203.

Next, the light from objective lens 204 is directed through atelecentric stop 206 that is positioned at a focal plane of the lens204. The stop 206 includes an opening 208 positioned at a focal point ofthe lens 204 so that only light reflected from the cornea that wasinitially parallel to the axis of the objective lens is allowed to passthrough the opening 208 and be received on the video image plane 210 ofa detector 212. As shown in FIG. 1, additional optics, such as a beamscanning system 216, beam combiner 218 and beam splitter 220, can beused to direct the reflected light 214 toward the lens 204.

Applying the above principles to detection system 200, one or moreconcentric (relative to the axis of laser beam from optical head 104,which is collinear with the axis of the objective lens, 204, in FIG. 2)diverging beams of light 201 are directed from the ring sources of lightsource 203 toward the cornea of the eye 102. If the cornea wereperfectly spherical in shape, then the beams of light 201 which reflectfrom the cornea into a direction parallel to that of the objective lens204 would pass through the telecentric stop aperture 208 and form imagesof the discrete LEDs in the concentric rings of light on the video imageplane 210. As shown in FIG. 2, a processor 230 analyzes overall image tofind the positions of each discrete LED 202 from the two concentric LEDrings.

For an average human cornea, with a radius of curvature of 7.8 mm, thesystem geometry is such that the diameters of the two concentric ringsof LEDs which are imaged by the telecentric viewing system areapproximately 2.3 mm and 1.65 mm, respectively, as shown in FIG. 3. Forcorneas of different radii of curvature, the size of the reflected ringswill differ and a determination of the size of the image of thereflected concentric rings of LEDs 202 on the telecentric cameradetector 212 is used to determine the radius of curvature of the cornea.If the cornea is astigmatic, the cornea's shape will deviate slightlyfrom that of a perfect sphere in such a way as to cause the image of thereflection of the ring sources to have a nearly elliptical shape. Basedon the measurement of the positions of the centroids of the discreteLEDs 202 which include the two concentric rings, the shape and size ofthe two circular or elliptical LED patterns formed on the video imageplane 210 is determined by the processor 230, using standard numericalmethods such as those described in Turuwhenua, Jason, “An Improved LowOrder Method for Corneal Reconstruction”, Optometry and Vision Science,Vol. 85, No. 3, March 2008, pp. E211-E218. From these data, thecurvature of the cornea along the direction of a steep and shallowmeridian, i.e. the “K values”, and the “clock” angle of the axes of thesteep and shallow meridian with respect to the standard eye-fixedcoordinate system, described above, can be determined by a processor. Ifonly the astigmatism axis is needed, a simple method of extracting itfrom the reflected images is to determine the angles of the semi-majoraxes of the ellipses using a simple least squares curve fittingtechnique.

The choice of geometry to cause the reflected diameters of the rings ofLEDs 202 to fall into the roughly 1.5 mm to 3 mm range results in anastigmatism (and corneal shape) measurement that is accurate for thecentral 3 mm of the cornea. Such a central region-biased measurement ofoptical power results in better vision for most patients over a varietyof lighting conditions and patient activities (ref). (For some eyes theoptical power of the cornea is quite non-uniform; the average opticalpower over a small central region may differ significantly from theaverage power averaged over, for example, a 6 mm to 7 mm diametercircular region centered on the optical axis of the cornea.)

Note that the incorporation of a high quality keratometer 250 into afemtosecond ophthalmic laser, being used as laser 104, addresses theproblem of higher variability in clinical refractive outcomes resultingfrom variability in measurement of patients' corneal K values and axesof astigmatism arising from use of different types of instruments forthat purpose. For purposes here, femtosecond ophthalmic laser means alaser used in ophthalmology for making incisions in the eye using themechanism of photodisruption. Such lasers have pulse widths that aregenerally between 100 femtoseconds and 10,000 femtoseconds. Theimprovement in clinical outcomes can be achieved in one of two ways.First, the built-in keratometer could be used for measuring the K valuesand axes of astigmatism of all patients at the time of the procedure andthose results be used for determination of the spherical and cylindricalpower in the IOL to be used for treatment. In this way, all variabilitydue to variation in measurement of these parameters with different typesof optical power measuring instruments would be eliminated. The lensconstants determined by the method described above would account forother factors, such as surgical technique/IOL characteristics, but wouldnot be subject to variability associated with optical power measurement.

Alternatively, the built-in keratometer could be used in conjunctionwith a standalone keratometer of the same type of design to reducevariability in the measurement of axis of astigmatism. This use of thebuilt-in keratometer in conjunction with a stand-alone keratometer ofthe same design for pre-operative measurements, recognizes that themeasurement of K values and axis of astigmatism depend on the type ofoptical design used. Although the K values and axis of astigmatismmeasured on a given eye by all types of measuring instruments will besimilar, differences in reported values may vary significantly.Instrument-to-instrument variation may be due to the region of thecornea measured by an instrument (for example one instrument may measureoptical power over the central 2.5 mm of the cornea; another may measureover 3.5 mm), the type of illumination source used (for example Placidorings versus rings of discrete LEDs), how the data is analyzed, etc. Theeffect of an error of as little as 10° in treatment of astigmatism axisis a 30% under correction of the astigmatism (A M Fea, et al, Eye 20,764-768 (2006)).

In this use of the present invention, the corneal optical power of apatient undergoing a cataract treatment with associated correction ofastigmatism would be measured on a particular type of standalonekeratometer, for example the keratometer sold under the tradenameLenStar LS900 by Haag Streit of Bern, Switzerland). The K values of thepre-operative measurement would be used for determination of IOLspherical and cylindrical optical power. At the time of surgery, withthe patient on a gurney under the femtosecond laser, the built-inkeratometer would be used to measure the axis of astigmatism of thepatient's cornea. As described above, this measurement of axis, with thepatient lying horizontally, is needed to compensate for cyclotorsion ofthe patient's eye between the pre-operative keratometer measurement madewith the patient in a sitting position and that measured in theoperative position of the patient, lying on a gurney. The built-inkeratometer would be designed in all significant aspects to measure Kvalues and axis of astigmatism in the same manner and to produceidentical results (except for those associated with cyclotorsion) as thepre-operative, standalone keratometer. Therefore any bias in measurementof astigmatism axis from one type of measurement instrument to anotheris eliminated and the treated axis is as near as possible to the correctastigmatism axis of the patient is used to treat the astigmatism withthe best possible clinical refractive outcome.

Note that the previously mentioned bias in measurement would also bereduced or eliminated in the case where a Placido ring system asdescribed in U.S. patent application Ser. No. 13/017,499 is incorporatedinto a treatment laser and such a built-in system is used to measurecorneal K values and axes properties of the eye in a manner as describedabove with respect to the built-in keratometer. And as above, such abuilt-in Placido ring system, used in conjunction with a standalonePlacido ring system of essentially the same design could be used in thesame manner and with the same benefits as is described above the builtin and standalone keratometer systems.

After the measurements of the rings of LEDs 202 previously described aremade by systems 200 and 300, the optical head of treatment laser 104 ismoved directly upward, out of the way, to allow access to the patient'seye 102 for application of a suction ring. In operation, a suction ring(not shown) is applied manually to the patient's eye 102. After thesuction ring is applied, the optical head of treatment laser 104 isdocked, using the previously described joystick. Since the patient's eye102 has not been moved and since the treatment laser 104 and theastigmatism measuring systems 200 and 300 are aligned to each other, thetreatment laser 104 can now be used to correct or reduce the astigmatismof the eye 102, based on the previously described astigmatism axisdetermination and/or the corneal shape determination, using limbalrelaxing incisions (LRIs) or LASIK, aligning the astigmatism treatmentto the measured axis of astigmatism.

The above described alignment system and process can also be applied toprocedures that involve implanting a toric intraocular lens (IOL) totreat astigmatism. Note that IOLs are synthetic lenses implanted intothe capsular bag in the eye, after a cataractous lens is removed. TheIOL restores vision by replacing partially opaque cataractous lens witha clear lens of appropriate power. A conventional IOL has only sphericalpower. A toric IOL has both spherical and cylindrical power and can thuscorrect astigmatism in the eye.

In the case when a toric IOL is to be subsequently implanted to treatastigmatism, the treatment laser 104 can be used to mark the axis ofastigmatism for later use in aligning the axis of astigmatism 410 (shownin FIG. 4) of the IOL 405 (with haptics 406 used for anchoring IOL 405in the capsular bag), with the marked axis of astigmatism of the eye102.

In cataract procedures, a round opening is manually torn or cut by alaser in the crystalline lens anterior capsule. The cataractous lens isremoved through the opening and an IOL is placed into the capsular bag,generally centered behind the capsular opening. The treatment laser 104can be used to cut a small “tag” as part of the circular capsulotomy400. The “tag” provides a visible reference mark along which the axis ofastigmatism of the IOL 410 can be aligned. As shown in FIG. 5, the“tags” 430 in the capsular openings can be positioned inwardly oroutwardly. The “tag” is cut in a smooth curve along the capsulotomy cutto avoid risk of radial capsular tears during the cataract procedure.Possible smooth shapes of the “tags” are shown schematically in close-up425. This method of marking the astigmatism axis by incorporating a“tag” in the capsulotomy allows the astigmatism mark, i.e. the “tag” tobe ideally placed for use in aligning the astigmatism axis of the IOL.The “tag” is in the immediate vicinity of the astigmatism mark on theIOL and may in fact be directly over the astigmatism axis mark on theIOL, avoiding any errors in registration which might occur when aligningthe IOL mark with, for example, an ink mark on the sclera, aconsiderable distance from the IOL. In summary, the “tag” provides avisual marker so that the surgeon implanting a toric IOL can line up theastigmatism axis of the IOL with marked axis of astigmatism of the eye102.

To avoid any possible distortion of the astigmatism axis of the eye 102which might occur when the a suction ring is placed on the eye 102 fordocking with the optical head of the treatment laser 104, a small mark,for example a line, could be made by the laser in the center of the lenscapsule immediately after the astigmatism axis was measured as describedabove. Then, after affixing the suction ring and docking the eye 102 tothe optical head, the marks in the center of the capsule could be used,either manually or using automatic image recognition techniques builtinto a computer program, to set the position of the “tag”—markedlaser-cut capsulotomy for use in the toric IOL implantation.

Still another alternate method of marking the astigmatism axis with thetreatment laser would entail shooting several laser shots, either atfull or reduced energy at the position of the astigmatism axis at thelimbus to make a persistent visible reference mark.

Since the x, y position of the optical head of the treatment laser 104is pre-aligned during the astigmatism axis measurement process, verylittle adjustment is needed to dock the optical head to the suctionring. Note that the telecentric viewing system 200 is also used as ageneral viewing system, to assist the laser system associated with theoptical head of the treatment laser 104 when the optical head is dockedto the suction ring.

Use of the measuring system 250 built in to the above described lasersystem 100 is advantageous. For example, the measuring system 250 wouldallow measuring the astigmatism axis in situ, while the patient is lyingon the treatment bed, just in advance of the laser treatment—thuseliminating the need for pre-operative eye marks. In the case ofperforming limbal relaxing incisions, the automatic measurement of theastigmatism axis by system 100 increases the accuracy of the placementof the limbal relaxing incisions, thereby improving the efficacy of thetreatment. The method can also be used in conjunction with the laser tomark the astigmatism axis for cyclotorsional registration of a toricIOL.

Despite the benefits of the method in convenience and more accurate,automatic placement of the treatment axis for astigmatism, and theadvantage of reducing clinical outcome variability by consistently usinga built in measurement system, or built in measurement system inconjunction with a pre-operative standalone system of the same design,to eliminate variability in clinical outcomes caused by determination ofIOL, lens constants with different measurement systems of differentdesign types, there is no laser astigmatism treatment device whichcurrently incorporates an astigmatism measuring system into the device.The present invention eliminates the need for manually marking the eyeand circumvents the inaccuracies inherent in manual placing of marks andthe dispersion of the ink marks by the eye's tear film; in addition, itprovides a means to more accurately determine IOL lens constants toreduce clinical outcome variability. The integral astigmatismmeasurement, in combination with use of marks made by the treatmentlaser can be used to mark the axis of astigmatism for later registrationof a toric IOL or for any subsequent refractive treatment of the eyerequiring knowledge of the axis of astigmatism.

Since the measuring device is built into the optical head of thetreatment laser 104, the alignment of the measuring 100 to the eye 102reduces the time needed later to align the eye to the laser treatmentsystem. The system 100 also makes dual use of a camera 212 and ringlight sources 202 for both the astigmatism measurement and for generalviewing of the eye during the eye docking and lasing parts of theprocedure.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

I claim:
 1. A method of placing a toric intraocular lens in a human eye,the method comprising: a. determining an axis of astigmatism of an eyehaving a cataractous lens; b. using a laser beam to perform acapsulotomy in the anterior lens capsule; whereby the laser beam cuts acapsular opening in the anterior lens capsule; wherein the capsularopening comprises a tag aligned with the axis of astigmatism; c. the taghaving slow curves without sharp edges, whereby the risk of radialcapsular tears is avoided; d. removing the cataractous lens, whereinradial tearing of the capsular opening is avoided; e. determining theaxis of astigmatism for a toric intraocular lens; and, f. inserting thetoric intraocular lens through the capsular opening into the lenscapsule and aligning the axis of astigmatism for the toric intraocularlens with the tag; wherein radial tearing of the capsular opening isavoided.
 2. The method of claim 1, wherein the tag is positionedinwardly of the capsular opening.
 3. The method of claim 1, wherein thetag is positioned outwardly of the capsular opening.
 4. The method ofclaim 2, wherein the capsular opening is in part circular.
 5. The methodof claim 3, wherein the capsular opening is in part circular.
 6. Amethod of placing a toric intraocular lens in a human eye, the methodcomprising: a. determining an axis of astigmatism of an eye having acataractous lens; b. using a laser beam to perform a capsulotomy in theanterior lens capsule; whereby the laser beam cuts a capsular opening inthe anterior lens capsule; wherein the capsular opening comprises a tagaligned with the axis of astigmatism; c. the tag having slow curveswithout sharp edges, whereby the risk of radial capsular tears isavoided; d. removing the cataractous lens; e. determining the axis ofastigmatism for a toric intraocular lens; and, f. inserting the toricintraocular lens through the capsular opening into the lens capsule andaligning the axis of astigmatism for the toric intraocular lens with thetag.
 7. The method of claim 6, wherein the tag is positioned inwardly ofthe capsular opening.
 8. The method of claim 6, wherein the tag ispositioned outwardly of the capsular opening.
 9. The method of claim 7,wherein the capsular opening is in part circular.
 10. The method ofclaim 8, wherein the capsular opening is in part circular.